Cut a piece of bacon into tiny pieces and cook. Add onion or shallots or scallions, and garlic. Add a tin of tomatoes if you want. Add rinsed french lentils and water (or stock, or wine, or whatever) to cover. Simmer until lentils are done and liquid is absorbed. Stir in a big dollop of dijon mustard. Taste for salt, acid--add lemon juice or vinegar if needed.
These get even better the next day.